#include <iostream>
using namespace std;

const int N = 100010;
int m;
int q[N], hh , tt = -1;

int main(){
    cin >> m;
    while(m --){
        string op;
        int x;
        cin >> op;
        if(op == "push"){
            cin >>x;
            q[++ tt ] = x;
        }
        else if(op == "pop" ) hh ++;
        else if (op == "empty") cout <<(hh <= tt ? "NO" : "YES") << endl;
        else cout << q[hh] << endl;

    }

    return 0;
}